Rotary printing presses with multiple printing stations having various degrees of computer controlled automation for processing continuous substrates or webs are known. The printing stations of such presses are often lined up in a row, with the stations being fixed to one another. Each station usually has its own gear train driven by a drive shaft common to all the stations. Each station has a printing mechanism including some form of rotatable printing element, such as a printing roller, for applying at least one component image of ink or other transferable image forming fluid at spaced apart locations along the length of the web (i.e., every revolution of the rotatable printing element). An impression mechanism having a backing face is used for backing the web while the image is being applied. For many rotary printing presses, such as rotary flexographic printing presses, the printing mechanism includes a printing plate mounted to the printing roller for applying the image to the web and an anilox roller with some form of inking mechanism (such as a metering roller or doctor blade assembly and ink reservoir) for dispensing measured amounts of ink or other such fluid to the printing plate. The impression mechanism is typically a rotatable impression cylinder roller. The gear train of each station usually drives the rotation of each of these rollers. With such multiple station presses, a single colored portion (i.e., component image) of a final composite image is printed at each station. Each of the component images are intended to be printed in register with respect to one another both longitudinally and transversely on the web.
Once one printing job has been completed, the printing mechanism of each of the printing stations (being used for the next printing job) will likely need to be changed or otherwise serviced in some way and repositioned for printing. For example, the printing roller may be replaced and the printing mechanism moved into a new position for printing. Such printing presses have to be shut down in order to prepare or set up the applicable printing stations for the next printing job. Oftentimes, the time it takes an operator to set up the printing press for the next printing job takes longer than the printing run itself. Every minute that the printing press is shut down in order to set up for the next printing job is time not spent running a printing job and generating revenue.
A number of prior printing presses have included automated systems for reducing set up times. These systems have varied in their degree of automation. Some of these automated set up systems have included positioning mechanisms for automatically moving rollers of the printing mechanism to and from various positions during preparation of the press for printing. Two such systems are disclosed in U.S. Pat. Nos. 4,413,560 and 5,060,570.
Attempts to reduce set up times have also included combining the printing mechanism of each printing station into a removable unit or cassette which may be replaced with another unit, previously prepared for the next printing job. See for example, U.S. Pat. Nos. 4,462,311 and 5,060,569.
While these prior efforts in reducing set up times have had some success, there is still a need for a more automated multiple station rotary printing press which can be changed from running one printing job to another in a shorter period of time.
A major problem encountered with multiple station rotary printing presses is consistently maintaining the quality of the images being printed, both print quality and image registration. Print quality problems, such as barring, have been known to chronically plague multiple station rotary printing presses. The registration of each partial or component image must be monitored and maintained to insure the quality of the final composite images. A number of prior printing presses have included computer controlled registration systems for automatically maintaining registration. The degree of success in consistently maintaining registration (i.e., positioning of the component images) over the length of the web has been found to generally vary from system to system. Inconsistency in maintaining print quality and registration control may increase the length of web that has to be scraped (i.e., the scrap rate) and limit the type of printing jobs that can be adequately run on a given press.
The assignee of the present invention has utilized a computer controlled registration system 500, illustrated in FIG. 22, for controlling longitudinal positioning of the component images on the web 501 (i.e., circumferential registration of the printing roller) in a previously manufactured multiple station flexographic rotary printing press 502 for processing narrow webs (i.e., webs having widths of about 19 inches (48 cm) or less). That flexographic printing press typically had two sets 503, 504 of six printing stations 505-510 and 511-516 with each set having one computer 550 controlling circumferential registration. Each station had a frame 517 with a gear train side 518 and an operator side 519 with the printing mechanism rollers 520, 521 therebetween. For each station, the shaft 525 mounting the impression roller 520 was powered off of a common drive shaft 526 through a worm gear set 527 located outside the gear train side of the station frame. The printing plate roller 521 of each printing station was individually rotated by the common drive shaft through a separate branch 528 of the station gear train driving a gear 535 on the printing roller 521. Circumferential registration of each station's component image was controlled by slowing down or speeding up the rotation of the printing roller 521 while maintaining the speed of the web 501 through the station. A single harmonic gear assembly 530, similar to that disclosed in U.S. Pat. No. 3,724,368, was connected within the separate gear train branch 528. The single harmonic gear assembly 530 was mounted on one end of a jack shaft 531 outside the gear train side 518 of the station frame 517 and downline of the impression roller 520. The jack shaft 531 was journaled at either end to the sides of the station frame. A gear 532 fixed to the impression roller shaft 525, between the worm gear set 527 and the gear train side 518 of the station frame 517, engaged and drove an outer gear 533 on the single harmonic gear assembly 530. The single harmonic gear assembly 530, in turn, rotated the jack shaft 531, driving a tooling gear 534 fixed to the jack shaft just inside the gear train side 518 of the station frame 517. The jack shaft tooling gear 534 drove another tooling gear 535 fixed to the shaft of the printing roller 521 through an idler tooling gear 536 mounted for free rotation about the impression roller shaft. Only the printing roller 521 was driven by the single harmonic gear assembly 530. All three tooling gears 534, 535 and 536 were spur gears, generally coplanar and located just inside of the gear train side 518 of the station frame 517. The single harmonic gear assembly 530 had a one percent difference in gear ratios. In order to compensate for this difference, the gear ratio between the impression roller gear 532 and the outer gear 533 on the single harmonic gear assembly 530 was made 100:101. A standard DC motor 537 was connected to a drive shaft 526 inside the single harmonic gear assembly which, when activated caused the jack shaft 531, and thereby the printing roller 521, to rotate at a different speed than the impression roller 520 or the common drive shaft 526. The impression roller 520 helped carry the web 501 through the printing station (505, . . . , 516). Thus, actuation of the single harmonic gear assembly 530 effected phase changes between the rotational speed of the printing roller 521 and the speed of the web 501.
To bring the component images of this earlier version of the assignee's Flexographic Rotary Printing Press into initial circumferential registration (i.e., preregistration), an operator would adjust the relative circumferential position of each printing roller 521 by activating the DC motor 537 of the appropriate single harmonic gear assembly 530 at switch 539. Preregistration was effected manually and took place with the press shut down. In controlling circumferential registration with the web 501 running through the press 502, the plate roller 521 of the first printing station 505 would print a mark 538 (a transverse bar) on the web 501 every revolution of the printing roller 521. The printing roller 521 at each subsequent printing station 506-516 downline from the first station had a separate mark 540 which rotated along with the printing roller. Two optical sensors 541, 542 were mounted to each station frame 517, one 541 for monitoring each of the web marks 538 as they passed by and the other 542 for monitoring the rotation of the station's printing roller mark 540. An encoder 544 was connected to the common drive shaft 526 of the printing press 502. This encoder 544 generated a certain number of electrical pulses every revolution of the common drive shaft 526 as well as the rollers driven thereby, including the impression rollers 520. Each computer 550 had a counter 551 for counting these pulses. Each sensor 541, 542 was basically a switch that turned on and off when a mark 538, 540 was sensed. Each computer 550 was programmed to read a pulse count directly from its counter 551 each time a mark 538, 540 triggered its respective sensor 541, 542 for any of the six stations connected to the respective computer 550. Each computer 550 was also programmed to read one pulse count and then the other pulse count for the pair of marks 538, 540 each revolution of the printing roller 521 at each of its six stations. These pulse count readings were then each stored in a register or section of memory 561, 562 respectively corresponding to the relative position of a mark 538, 540 for each respective station connected to the respective computer 550. After obtaining a pulse count for each mark from a station, the appropriate computer 550 subtracted the two numbers to obtain a difference count equal to the number of pulses between the two marks. This difference count was also stored in a register 563 for the respective station. The sequence in which the computer 550 acquired and analyzed the pulse count for the marks 538, 540 at each of the different printing stations depended upon the order in which each station's marks were sensed. The computer would not begin a new cycle of searching for the marks, acquiring pulse counts and analyzing the data at all six stations until the marks at each station for the previous cycle were analyzed or three unsuccessful attempts at searching for the marks had been made. If both marks at a given station were not sensed in one revolution, for whatever reason, the computer 550 was programmed to continue searching for up to three revolutions of the printing roller 521 before abandoning the search and starting a new cycle.
The setting of optimum circumferential position of each printing roller in a given set of stations relative to the web was stored in a corresponding location in a memory 555 in the respective computer 550 as a number of pulses (i.e., a count) between the sensing of the printing roller mark 540 and each web mark 538. This optimum position was subtracted from the difference count to produce an error value that was stored in a register 564 or memory location corresponding to the respective station. The optimum position of each printing roller 521 was a quality determination previously made by an operator. This error count was compared with a tolerance range value stored in a memory 556. If the pulse count between the marks fell outside of an acceptable range initially determined by the operator and stored in the memory 556 by the operator, the computer 550 sent a corresponding signal to a driver 565 that actuated the DC motor 537 on the appropriate single harmonic gear assembly 530 of the corresponding station to thereby effect a phase change and rotate the applicable plate roller 521 back into registration. In making these registration corrections, the appropriate DC motor 537 would be turned on by the applicable computer 550 at the beginning of a repeat length (i.e., the distance between successive web marks) and allowed to continue running for a period of time programmed to be approximately equal to the number of pulses (i.e., counts) the image was out of register. The period of time programmed to correspond to one count could be varied. Thus, each computer 550 acquired the data (i.e., the pulse count) for the marks 538, 540 at each of the six stations 505-510 and 511-516 in its respective set 503, 504, analyzed the data (i.e., compared it with the optimum count) and then made the appropriate corrections.
It is often desirable to subject a web to more than one printing run. For example, it may be desirable to run the web through a flexographic printing press, subject the web to an intermediate printing operation, and then reinsert the web through the flexographic printer for another printing run. When a web is subjected to multiple printing runs, the web is likely to go through dimensional changes which often vary along the length of the web. As the web changes dimensionally, so do the images previously printed on the affected areas of the web. Therefore, besides circumferential registration control, there is a need for a computer control system capable of making corrections for such dimensional changes during subsequent printing operations (i.e., reinsertion control).
The previously manufactured multiple station flexographic rotary printing press 502 of the assignee of the present invention included a reinsertion control system. In the prior reinsertion control system, a central computer took one or more readings of the registration errors from each operating printing station in the press and then averaged all of these values to arrive at a reinsertion error. The average of consecutive registration errors represented the repeated differences between the repeat length of the press and spaces between preprinted web marks (i.e., actual repeat lengths). This difference is attributed to dimensional changes in the web and is defined as the reinsertion error. The original web marks 538 printed during the initial printing run were sensed for the registration control during the subsequent printing runs. This central reinsertion computer was alternatively provided with the programming option of giving current readings more weight than older readings or weighing the readings from each station the same. Based on the average of these readings, the reinsertion control computer would simultaneously make the same reinsertion error correction for this average error at each operating printing station, on a continuous basis. The correction was applied as a signal that was added to the circumferential registration control signal. As with the prior circumferential registration control correction, the reinsertion corrections were made by circumferentially adjusting the appropriate printing roller 521 with the single harmonic gear assembly 530 driven by a motor responsive to analog pulse width control signals.
Notwithstanding the prior art, there remains a continuing need for an even more fully automated and cost effective multiple station rotary printing press that is able to even more consistently maintain print quality and image registration, even when the web is reinserted, and which takes less set up time to change from running one printing job to another.